In the figure shown there are two semicircles of radii r1 and r2 in which a current i is flowing. The magnetic induction at the centre O will be
The magnetic induction due to both semicircular parts will be in the same direction perpendicular to the paper inwards.
∴ B = B1 + B2 = μ0i4r1 + μ0i4r2 = μ0i4(r1+r2r1r2)⊗